The present invention is directed to an arrangement for the complete emptying of flat quartz tanks, or crucibles, filled with silicon melt, as used for the continuous, horizontal band drawing of silicon bands wherein carrier members contact the melt surface.
An example of a horizontal band drawing method is disclosed in European Patent Application No. 170 119. This method is referred to as the S-web, or supported web, method. By use of this method, silicon bands for solar cells can be produced continuously from a silicon melt with a high drawing speed (approximately 1 m/min).
Pursuant to this method, the silicon melt is located in a first flat, roughly rectangular, quartz tank having, for example, a length of 70 cm, a width of 15 cm, and a height of 1 cm. Another flat quartz tank, or crucible is connected to the first tank, that houses the silicon melt, by way of a connecting tube. The second quartz tank functions to melt silicon so that melted silicon is constantly available. During the duration of the process, the height of the silicon melt in the quartz tanks is approximately at a maximum of approximately 3 cm, and preferably 1 to about 2 cm.
After the conclusion of the drawing process, a residual melt having, for example, a height of 0.5 to 1.0 cm remains in the quartz tanks and in t he connecting tube. Because these quartz tanks are seated in supporting tanks of graphite that are surrounded by thermal insulation and heating devices, it is not possible to empty the silicon residue in the tanks by simply tipping the quartz tanks on their sides. It is, however, necessary to remove the residue silicon. When heat is no longer supplied to the tanks, the residual melt that remains therein, solidifies in the tanks and, due to the different dimensional changes of quartz and silicon, destroys the quartz vessels as it cools.
One possible method of removing the residual melt from the tanks or crucibles is to try to absorb the residual melt into carbon wool. This type of removable, however, is extremely involved and is not especially economical. Moreover, this method can lead to the contamination of the quartz vessels with carbon.